Method of welding by induction heating



Aug 9, 1949. w. M. RoBERDs 2,478,640

METHOD OF WELDING BY INDUCTION HEATING VFiled June 14,y 1946 77k a4/W? JNVENTOR.

Patented Aug. 9, 1949 UNITED STATES PATENT OFFICE METHOD OF WELDING BY INDUCTION HEATING of Delaware Application June 14, 1946, Serial No. 676,647

5 Claims. (Cl. 219-10) This invention relates to a new and improved method of welding thick walled tubing by induction heating. In Patent No. 2,024,906, December 17, 1935, Edward Bennett describes a system for applying radio frequency heating currents to the adjacent edges of a conductive material for the purpose of bringing them to a temperature suiiicient to cause them to unite. In this patent currents are induced by a closely spaced single turn inductor coil which is removed from the work when the jloint has been completed. This method has the disadvantage that heat which is inherently generated in the applicator coil serves no useful purpose and its application to the Welding of materials of certain shape make subsequent removal of the applicator coil somewhat diflicult. It is the primary purpose of this invention to overcome the disadvantages of the prior art by applying radio frequency heating currents to the adjacent edges or faces of a workpiece which is to be welded by a single turn split ring applicator coil which is heated to the same temperature as the work piece and which subsequently becomes a part of the welded joint.

In practicing this invention, the applicator coil is a split ring shaped like a common lock washer, having a diagonal cut and being slightly sprung so that the adjacent ends of the applicator are not in contact. Temporary connections are made to the open ends of the applicator coil for the application of the radio frequency heating current. The applicator has the same general shape and dimensions as the work pieces to be joined and after sufiicient heating has been accomplished the work pieces are brought into contact with the applicator so that'a wel-ded joint is effected. The temporary connections are then re.- moved and the applicator coil becomes a unitary part of the welded joint.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention both as to its lorganization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which Figure 1 is a schematic view illustrating this invention;

Figure 2 is a perspective View of a single turn, split ring applicator, and

Figure 3 illustrates the method of cooling the radio frequency conductors to concentrate the heat in the applicator coil.

Referring to Fig. 1, the application of this invention in welding the adjacent edges of two pieces of steel tubing l and 3, a single turn split ring applicator coil 5, having the same inner and outer diameter as the tubes to be joined, is placed in line with and between the abutting edges of the workpiece, and spaced approximately t4 of an inch on either side. High frequency currents are applied to the applicator coil from a radio.

frequency generator 'I through an impedance matching transformer 9 by means of temporary conductors which are pressed or welded adjacent the open ends of the applicator coil, as shown at points Il and I3 respectively. The radio frequency generator is provided with the necessary A. C. and D. C. energizing currents by a suitable power supply I5 through an overload relay il whose function is to disconnect the high voltage potential from the generator when the plate current exceeds a predetermined value.

As is well known, high'frequency currents tend to flow =on the face of an applicator coil when the workpiece in which currents are induced is in close proximity thereto. This is known as the proximity effect and is described in the patent f referred to above. As a result, the induced radio frequency currents flowing in the edges of the workpieces l and 3 which are adjacent to the applicator coil 5 are limited to the region immediately adjacent the applicator coil. The heating effect is therefore applied substantially only to the region where it is needed to bring the ends of the workpieces to a suitable welding temperature. At the same time, the current flowing in the applicator coil itself causes it to be brought to substantially the same temperature. Depending upon the radio frequency power applied, the welding temperature may be reached in a relatively short time, thus limiting the heat to the desired region and preventing its loss by conduction through the workpieces.

Referring to Fig. 2, it will be noted that the split ring applicator 5 is provided with two temporary connectors I 9 and 2i which are brazed or Welded to the open ends of the applicator ring, and are preferably positioned as near the ends as possible. The temporary connectors are preferably of the same cross-sectional area as the applicator ring itself and should be highly conductive to electrical currents but a relatively poor heat conductor so that the temporary connections will not cause cold spots in the applicator ring, and so that they will be heated to the same vdegree as the ring itself. For this reason copper is not preferred, since it is highly conductive of heat and will tend to cool the applicator ring form a strong bond. When this occurs the applicator ring closes and its open edges are brought into contact and are similarly bonded. This short-circuits the applicator ring, produces a momentary overload on the radio frequency generator, and causes the overload relay l1 to disconnect the high frequency potentials toavoid damaging the generator. Alternatively, the high voltage potential may be removed from the generator just before or concurrently with the movement of the work pieces either manually or automatically byy means of a switch actuated by the movement of either one or both of the work pieces. Y

Y After the Weld has been completed, the joint may-be cooled rapidly if desired, after which the temporary connectors I9V and 2l are sawed od and the weld is completed.

- In order to concentrate the heating in the applicator electrode an-d the inner portions of thetemporary connectors, it maybe desirable to cool the' leads from the secondary to transformer 9. A method of accomplishing this isillustrated in Fig. 3, to which reference isV now made. The temporary connectors |-9 and 2| are shown connected to the applicator coil 5. Electrical connections to the secondary 23 of the coupling transformer 9 are made by connecting lugs 25 and 21 which are provided with suitable recesses to receive the outer ends of the temporary connectors and which may be held in placeV by thumbscrews 29 and 3l. The connecting lugs are pressed or welded to a' double hollow tube which constitutes'the secondary 23 Vof the transformer. This tubing may consist, for example, of two copper tubes pressed' together so as to constitute an ingoing and outgoing passage for cooling fluid. Within the `connecting' lugs 25 and 2l there is provided a small chamber through which the coolinif;Y fluid circulates'before returning to the Y secondary winding. The secondary is preferably grounded at its midpoint and the cooling iiuid is admitted into the tubes at this point. Cooling fluid is circulated from a reservoir by means of a pump and a cooling fan or other cooling system may be employed as desired. The pump, reservoir and cooler are illustrated diagrammatically at reference numeral 33.

There has thus been described a method of joining abutting edges of a workpiece by means of radio frequency currents induced in the workpiece by a split ring applicator coil which comprises placing the applicator between the edges to be joined, applying radio frequency currents to the applicator to heat both the applicators and the adjacent edges ofthe work piece and pressing the work piece against the applicator to cause it to unite with the workpiece and become a permanent part thereof.

What I claim is:

I. The method of joining opposed spaced edges ofv electrically conductive work pieces by means of radio frequency currents induced in said workpieces by induction heating applicator means, which comprises forming an induction .4 heating applicator of electrically conductive material which will unite with the material of the Workpieces and in a split ring conforming in size and shape with said edges, placing said applicator between and in spaced relation to the edges to be joined, the plane of the applicator ring being substantially-parallel with said edges, applying radio frequency currents to said applicator to heat the applicator by currents flowing therein and the adjacent edges of said workpieces, by currents induced therein and pressing said edges against said applicator to cause said applicator to unite with said workpieces and become a permanent part thereof.

2. The n ietl'iod of joining opposed spaced edges of electrically conductive workpieces by means ofradio, frequency currents induced in said workpieces by induction heating applicator means, which comprises forming an induction heating applicator of electrically conductive material which will unite with the material of the workplaces and in a split ring conforming in size and shape with said edges, placing said applicator between and in spaced relation to the edges to be joined', the plane of the applicator ring being substantially parallel with said edges, temporarily connecting a source of radio' frequency power to said applicator, causing radio frequency current fromV said power source to flow through said applicator to induce heating currents in the adjacent edges of said workpieces while heating said applicator, moving said workpieces into contact with said applicater to cause said applicator to unite with said workpieces, and removing said temporary connections.

3,. The methody Y ci joining opposed spaced edges of electrically conductive workpieces by means of radio frequency currents induced in said worlrpieces by induction heating applicator means, which comprises forming an induction heating rapplicator of electrically conductive material whichl will unite with the material of the workpieces and in a split ring conforming in size and shape with said edges, placing said applicator between and in, spaced relation. to the edges to be joined, the plane of the applicatorring being substantially parallel with said edges, temporarily connecting a source of radio frequency power to said applicator, causing radio frequencyA current from said power source to iiow circumferentially around said applicator to induce heating currents in the adjacent edgesV of said workpieees while heating said applicator to substantially the same temperature, moving the opposed edges of said workpieces together against said applicator to cause said applicator to unite with said workpieces, and removing said temporary connections.

4. TheV method of joining Opposed spaced edges of electrically conductive workpieces by means of radio frequency currents induced in said workpieces by induction heating applicator means, which comprises forming an induction heating applicator of electrically conductive material which will unite with the material of the workpieces and in a split ring conforming in size and shape with said edges, placing said applicator between and in close proximity to the edges to be joined, the plane of the applicator ring being substantially parallel with said edge-s, temporarily connecting a source of radio1 frequency power to said applicator, causing radio frequency currents to ow through said applicator to heat said applicator While inducing 5. heating currents in said workpieces, moving the edges of said workpieces together against said applicator to cause said applicator to unite with said workpieces, discontinuing the application of said radio frequency currents, and removing said temporary connections.

5. The method of joining opposed spaced ends of two cylindrical electrically conductive members by means of radio frequency currents induced therein `by induction heating applicator 10 of radio frequency power to the ends of said 20 applicator, causing radio frequency currents to ow through said applicator to heat said applicator while inducing heating currents in said members, moving said members together against said applicator to cause said applicator to unite with said members, discontinuing the application of said radio frequency currents, and removing said temporary connections.

WESLEY M. ROBERDS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,572,740 Mattice Feb. 9, 1926 1,936,309 Northrup Nov. 21, 1933 2,024,906 Bennett Dec. 17, 1935 2,066,668 Bennett Jan. 5, 1937 2,329,944 Schakenbach Sept. 21, 1943 2,408,229 Roberds Sept. 24, 1946 

